In general, the present invention relates to percutaneous transluminal devices and methods which are used to treat obstructed (sclerotic) vessel lumina in humans. In particular, the present invention is an improved method for fabricating stents or prostheses. In addition, the improved method employs a novel apparatus.
Cardiovascular disease is commonly accepted as being one of the most serious health risks facing our society today. Diseased and obstructed coronary arteries can restrict the flow of blood and cause tissue ischemia and necrosis. While the exact etiology of sclerotic cardiovascular disease is still in question, the treatment of narrowed coronary arteries is more defined. Surgical construction of coronary artery bypass grafts (CABG) is often the method of choice when there are several diseased segments in one or multiple arteries. Conventional open heart surgery is, of course, very invasive and traumatic for patients undergoing such treatment. In many cases, less traumatic, alternative methods are available for treating cardiovascular disease percutaneously. These alternate treatment methods generally employ various types of balloons (angioplasty) or excising devices (atherectomy) to remodel or debulk diseased vessel segments. A further alternative treatment method involves percutaneous, intraluminal installation of one or more expandable, tubular stents or prostheses in sclerotic lesions. Intraluminal endovascular prosthetic grafting is an alternative to conventional vascular surgery. Intraluminal endovascular grafting involves the percutaneous insertion into a blood vessel of a tubular prosthetic graft and its delivery via a catheter to the desired location within the vascular system. The alternative approach to percutaneous revascularization is the surgical placement of vein, artery, or other by-pass segments from the aorta onto the coronary artery, requiring open heart surgery, and significant morbidity and mortality. Advantages of the percutaneous revascularization method over conventional vascular surgery include obviating the need for surgically exposing, removing, replacing, or by-passing the defective blood vessel, including heart-lung bypass, opening the chest, and general anesthesia.
Stents or prostheses are known in the art as implants which function to maintain patency of a body lumen in humans and especially to such implants for use in blood vessels. They are typically formed of a cylindrical metal mesh which can expand when pressure is internally applied. Alternatively, they can be formed of wire wrapped into a cylindrical shape. The present invention relates to an improved method of manufacturing stents.
Stents or prostheses can be used in a variety of tubular structures in the body including, but not limited to, arteries and veins, ureters, common bile ducts, and the like. Stents are used to expand a vascular lumen or to maintain its patency after angioplasty or atherectomy procedures, overlie an aortic dissecting aneurysm, tack dissections to the vessel wall, eliminate the risk of occlusion caused by flaps resulting from the intimal tears associated with primary interventional procedure, or prevent elastic recoil of the vessel.
Stents may be utilized after atherectomy, which excises plaque, or cutting balloon angioplasty, which scores the arterial wall prior to dilatation, to maintain acute and long-term patency of the vessel.
Stents may be utilized in by-pass grafts as well, to maintain vessel patency. Stents can also be used to reinforce collapsing structures in the respiratory, biliary, urological, and other tracts.
As described in U.S. Pat. No. 4,776,337 issued to Palmaz, the cylindrical metal mesh shape is produced by laser cutting a thin walled metal tube. A laser is used to cut away all but the lines and curves of the mesh. The method of U.S. Pat. No. 4,776,337 is applicable for relatively large mesh shapes and for meshes whose lines are relatively wide. However, for more delicate and/or intricate shapes, the spot size of the laser is too large.
European Patent Application EP 0 709 067 A2 describes a stent fabrication method of preparing a flat pattern design, cutting the pattern in the flat sheet, deforming the sheet to cause the edges to touch, connecting at least the edges at least one point usually by a welding process, and then polish the finished product. The disadvantage of this process is that flat sheet must be deformed to form the final tubular configuration, and that there is a longitudinal attachment point which provides a discontinuous outer contour and a potential weak point for failure. Furthermore, the weld is metallurgically and chemically unstable and will degrade in the human body. In addition, this process requires several critical manufacturing steps which are eliminated by the present invention.
U.S. Pat. Nos. 5,514,154 and 5,421,955 describe a stent manufacturing process utilizing a computer controlled laser to selectively remove an etchant-resistant coating form a design resembling a stent. The use of a laser to selectively remove the etchant-resistant coating is a relatively expensive and complicated process. The laser must be linked to a computer controlled X-Y movement system that must precisely control the rotation and movement of the laser for stent fabrication. Variances in this process will transcend into variability in the fabricated stent. The present invention neither requires the use of an expensive laser system nor the complex movement system.
It is, therefore, an object of the present invention to provide a stent fabrication method which can produce stents with relatively intricate, delicate and detailed designs from a tubular member which negates the disadvantages of the prior designs.
In addition, it is a further object of the present invention to provide a method of fabricating a stent which involves processing a tubular member whereby no connection points to join the edges of a flat pattern are necessary.
The present invention involves a method of fabricating a stent by processing a tubular member. During the fabrication process, a novel apparatus is employed to expose a coated tubular member to a precise pattern of UV light dictated by a specifically designed film which moves over the tubular member as it is rotated.
The method of manufacture includes the steps of first electro-cleaning the tubular member with an appropriate solution. The tubular member comprises stainless steel, platinum, titanium, tantalum, gold alloy, or a gold/platinum alloy, but any number of metallic elements or polymeric materials can be employed.
Once the tubular member is cleansed of contaminates, the outer surface is uniformly coated with a photo-sensitive resist. Optionally, a coupling agent may be used to facilitate the bonding of the photo-sensitive resist to the tubular member. The coupling agent is not essential in that some tubular member compositions bond directly to the photo-sensitive resist solution without the need for a coupling agent.
This coated tubular member is then placed in an apparatus designed to rotate the tubular member while the coated tubular member is exposed to designated pattern, of ultraviolet (UV) light. The apparatus controls the exposure of the coated tubular member by utilizing a photographic film with a specified computer generated imprinted configuration, transferring the UV light in the specified pattern to the coated tubular member. The UV light activates the photo-sensitive resist causing the areas where UV light is present to expose (cross-link) the photo-sensitive resist. The photo-sensitive resist forms cross links where is it exposed to the UV light thus forming a pattern of hardened and cured polymer which mimics the particular stent design surrounded by uncured polymer. The film is adaptable to virtually an unlimited number of intricate stent designs. The process from the apparatus results in the tubular member having a discrete pattern of exposed photo-sensitive material with the remaining areas having unexposed photo-sensitive resist.
The exposed tubular member is immersed in a negative resist developer for a specified period of time. The developer removes the relatively soft, uncured photo-sensitive resist polymer and leaves behind the cured photo-sensitive resist which mimics the stent pattern. Thereafter, excess developer is removed from the tubular member by rinsing with an appropriate solvent. At this time, the entire tubular member is incubated for a specified period of time, allowing the remaining photo-sensitive resist polymer to fully cure (harden) and attach to the surface of the processed tubular member. The tubular member can be incubated at room temperature or can be exposed to a heat source in the range of 100 to 400 degrees Celsius.
The processed tubular member is then exposed to a electro-chemical etching process which removes uncovered metal from the tubular member, resulting in final tubular member or stent configuration.
This process can lend itself to virtually an unlimited number of stent designs and configurations. By modifying the film and employing the identical process one can fabricate a variety of stent designs.
The present invention will be understood and appreciate more fully from the following detailed description taken in conjunction with the drawings.